Posted
by
timothy
on Sunday January 30, 2011 @01:17PM
from the no-this-is-me-in-a-nutshell dept.

An anonymous reader writes "In a feat of modern-day alchemy, atom tinkerers have fooled hydrogen atoms into accepting a helium atom as one of their own, reports New Scientist. Donald Fleming of the University of British Columbia in Vancouver, Canada, and colleagues managed to disguise a helium atom as a hydrogen atom by replacing one of its orbiting electrons with a muon, which is far heavier than an electron. The camouflaged atom behaves chemically like hydrogen, but has four times the mass of normal hydrogen, allowing predictions for how atomic mass affects reaction rates to be put to the test."

As I recall, the poor muon has an average lifetime of something like 2 microseconds. We might see some interesting theoretical chemistry come out of this (the reaction-rate question) but it looks like we'll end up a little light on practical applications of muons in chemical compounds.

I remember that much past interest over muons and hydrogen has been around muon-catalyzed fusion. As you say, the muons are quite short-lived, which prevents them from catalyzing enough H-H fusions to get to breakeven. And then there was the alpha-sticking problem, whereby helium nuclei products then grab the muons, thus stealing them away from the process.

Check out ultra-dense deuterium, though. It's some kind of exotic form of matter, and there have recently been some tantalizing glimpses of it in nano-sized clumps.

Yeah, like this. Sorry I didn't see your post. My Ph.D. advisor, Larry Biedenharn, was heavily involved in this for four or five years, but as I said, it didn't quite pan out partly because of the sticking problem, partly because one can only make muons at something like 10% energy efficiency (remembering from the many seminars we had on this back in those days, not looking up the exact numbers). Larry always thought they'd do it with a special "breeder" fission reactor to get the muons for free as a side-effect of making energy the other way to boost fission returns by a factor of 50% or so, but this never happened AFAIK.

It is still an open problem -- the question is really is there an environment where the He sticking problem is suppressed (they didn't find one, but I doubt the search was exhaustive) and is there any way to produce muons at higher efficiencies -- say some sort of resonant conversion of electrons into muons that beats 5-10%. My recollection is that they were within a factor of ten, maybe even within a factor of 2-3 of break even but couldn't quite find a way over the hump. They know way more about neutrinos now than they did back then -- one wonders if anybody is even thinking about it any more.

To be more specific, the molecular weight of normal He to He with one muon attached is roughly 4.1/4.0. The change in pitch relative to breathing He should be the square root of that ratio, which is a change of about 1.2%. For someone with absolute pitch, it may be possible to hear the difference of tone of a musical instrument. But I doubt anyone will hear a difference when a person speaks.

By the way... I think the commentator in the attached perspective (http://www.sciencemag.org/content/331/6016/411.full) gets the born-oppenheimer approximation wrong... he states that :

"The BO approximation makes possible the practical application of quantum mechanics to all of molecular science. As the arrangement of the nuclei changes, the BO approximation postulates that the electrons will remain in a particular quantum state. "

When the BO approximation is the opposite : The atoms DONT move while the electrons DO (relatively speaking) because of their vast difference in mass. That is... the electrons are little bullets whizzing around at top speed, whereas the atoms are massive aircraft carriers in terms of mass (note: this is not meant to be even a remotely accurate analogy, but it's the general idea). You'd think that SCIENCE, of all journals, would get the Born-Oppenheimer approximation right !

Note: That in the second step of a typical quantum mech. calculation (e.g. a geometry optimization), you then use the average field generated in the first part to move the atoms (if they need to move in the particular calculation). Then you iterate to self-consistency.